About the where you should start sliding on the rail for lipslides, true there's not proper or improper way, a lot of people just think it looks better (myself included)
There's more material out on the web in regards to snowboarding so check out those links like I said before -> http://youtu.be/sGSdL_fpqTw?t=5m55s

Hey Sergio,
from what you wrote, you are correct. Unfortunately the above diagram is not correct and the names actually come from skateboarding. Because of the skateboard trucks, you also run into tail/nose slides, blunts, and grinds (trucks), but for the basics, you've got it.

Only one question,. does it changes the name depends on where you access to the rail?

some friend is telling me a lipslide is only when you start it at the middle of the rail, never at the beginning .

is that correct?

thanks again!

My personal opinion is it is only a lipslide if it is very clearly a iipslide. This doesn't rule out hitting the rail from the beginning but if you approach a rail from straight on, I would not call it a lipslide. If you approach at an angle and ollie into a lipslide and happen to land at the start of the rail, you're good.

Just my opinion but I can see where someone would say not to hit the start of the rail which I think in most cases doesn't happen anyways.